Bill Sweet­man Tech­ni­cally Speak­ing

OB­SER­VA­TIONS FROM THE FRONT LINES OF AEROSPACE

Air & Space Smithsonian - - Front Page -

Can re­us­able launch­ers be so hard?

ELON MUSK’S COM­PANY Spacex started 2015 with an at­tempt to re­cover the first stage of its Fal­con 9 rocket. If it suc­ceeds— enough has been demon­strated so far to make that likely— Spacex will be­come the first to launch a rocket-pow­ered first stage to or­bit, then land it un­der con­trol.

The Fal­con 9 will be the sec­ond partly re­cov­er­able launch ve­hi­cle. The first was the space shut­tle, but it has been re­tired in fa­vor of the ex­pend­able rock­ets it was sup­posed to re­place. “Within a decade from now most of Amer­ica’s in­ven­tory of con­ven­tional throw­away launch rock­ets will have been re­placed by a more el­e­gant and hope­fully cheaper lad­der to or­bit,” re­ported Flight In­ter­na­tional in 1975, back be­fore the or­biters had been built.

Some peo­ple will tell you that re­cov­er­ing a space launcher is so dif­fi­cult that the eco­nomics can’t work, and use as ev­i­dence the fail­ure of the shut­tle to de­liver its ad­ver­tised sav­ings and the col­lapse of other re­us­able space­plane projects.

In my view, a few or­ga­ni­za­tions could have made a re­us­able launcher work, and the rea­sons they failed were po­lit­i­cal rather than tech­ni­cal. The most in­flu­en­tial of those or­ga­ni­za­tions was NASA.

The space agency in­deed wanted to re­place all of Amer­ica’s rock­ets. That goal re­quired co­op­er­a­tion be­tween NASA and the Pen­tagon, the lat­ter fronting for the in­tel­li­gence com­mu­nity. But the co­op­er­a­tion pro­duced a shut­tle de­signed to launch a huge spy space­craft and re­turn it on short no­tice; the shut­tle ended up ca­pa­ble of car­ry­ing a 30-ton load and had big wings to make a long glide to its home base.

It was rather like the de­sign­ers of the Dou­glas DC-3 set­ting out, in 1935, to build the Boe­ing 707. The first de­signs for fully re­us­able shut­tles were mon­sters, so the goal was changed to partly re­us­able: A re­us­able or­biter was mated to a dis­pos­able ex­ter­nal fuel tank and re­us­able solid boosters. Even so, the space­craft’s air­frame re­quired un­tried, frag­ile ma­te­ri­als to pro­tect it from reen­try heat­ing.

By the time the Chal­lenger broke apart on launch, on Jan­uary 28, 1986, the Pen­tagon had walked away. The shut- tle—now the world’s most ex­pen­sive launch ve­hi­cle rather than its cheap­est—was part of a NASA triad, to­gether with the space sta­tion and hu­man space­flight. The sta­tion gave the shut­tle a mis­sion; to­gether, the sta­tion and shut­tle jus­ti­fied the as­tro­naut corps. Hu­man space­flight meant po­lit­i­cal sup­port, and all three pro­grams sup­ported a mas­sive work­force.

It was log­i­cal that any new re­us­able launch ve­hi­cle (RLV) should be more eco­nom­i­cal than the shut­tle. But new ideas were not eval­u­ated against the real shut­tle; they were com­pared to rosy prom­ises of a safer and more ef­fi­cient shut­tle that would be de­vel­oped a decade down the road.

The RLV ef­fort was con­se­quently based on the so­lu­tion that of­fered the best eco­nomics of all: a sin­gle-stageto-or­bit (SSTO) ve­hi­cle. No assem­bly re­quired; put the satel­lite in the pay­load bay, gas, and go. But it was beyond the state of the art. An SSTO had to ei­ther use a hy­per­sonic air-breath­ing engine or be a rocket ve­hi­cle car­ry­ing ten times its weight in fuel. Two at­tempts to build an Rlv—the Mcdonnell Dou­glas Delta Clip­per and the Nasa/lock­heed Martin X-33—had to com­pete with pa­per stud­ies of bet­ter shut­tles. Both were SSTOS and both failed.

A two-stage-to-or­bit (TSTO) re­us­able ve­hi­cle has emerged from many de­sign stud­ies as a good trade­off be­tween per­for­mance and tech­ni­cal risk. The idea was looked at most se­ri­ously for a few years in the late 1990s. In 2001, NASA and the Air Force even formed a “Oneteam” to look at fu­ture RLVS, with all sorts of in­ter­est­ing con­cepts on the ta­ble, al­most all of them un­manned TSTOS. But in Feb­ru­ary 2003 the shut­tle Columbia was de­stroyed on reen­try, con­firm­ing that the shut­tle could never be made safe. NASA promptly switched its ef­forts to a fu­ture space pro­gram that pre­served the shut­tle in­dus­trial base, the space sta­tion, and its as­tro­nauts.

If Spacex suc­ceeds and can rou­tinely re­cover un­dam­aged boosters, the com­pany will gain an eco­nomic ad­van­tage and in­spire others to fol­low suit. But if an RLV be­comes a re­al­ity, Nasa—de­spite be­ing the best funded space re­search agency in the world—will have had lit­tle to do with it. ■ ■ ■

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